Question

I have looked up in BSD code but got lost somewhere 🙁

the reason I want to check is this:

TCP RFC (http://www.ietf.org/rfc/rfc793.txt) sec 2.7 states:

“To provide for unique addresses within each TCP, we concatenate an internet address identifying the TCP with a port identifier to create a socket which will be unique throughout all networks connected together. A connection is fully specified by the pair of sockets at the ends.”

Does this mean: socket = local (ip + port) ?

If yes, then the accept function of Unix returns a new socket descriptor. Will it mean that a new socket is created (in turn a new port is created) for responding to client requests?

PS: I am a novice in network programming.

[UPDATE] I understood what I read @ How does the socket API accept() function work?.
My only doubt is: if socket = (local port +local ip), then a new socket would mean a new port for the same IP. going by this logic, accept returns a new socket (thus a new port is created). so all sending should occur through this new port.
Is what I understand here correct?

Answer 1

You are mostly correct. When you accept(), a new socket is created and the listening socket stays open to allow more incoming connections but the new socket uses the same local port number as the listening socket.

A connection is defined by a 5-tuple: protocol, local-addr, local-port, remote-addr, remote-port.

Therefore, each accepted connection is unique even though they all share the same local port number because the remote ip/port is always different. The listening socket has no remote ip/port and so is also unique.